The present invention relates to a control valve assembly for regulating the flow amount of exhaust gas or intake gas flowing through an internal combustion engine of an automobile, etc., by opening and closing a valve by linear motion.
With the operation of an internal combustion engine of an automobile, etc., exhaust gas or intake gas, which is a controlled fluid, flows and the flow amount of the controlled fluid is regulated by control valve assemblies. The flow amount of the controlled fluid may be regulated, for example, by an exhaust gas recirculation valve (hereinafter EGR valve) or by an idle speed control valve (hereinafter ISC valve), functioning as a control valve assembly.
FIG. 5 is a schematic structural diagram of a conventional EGR valve as shown in Japanese Utility Model Publication No. 6-14054, and FIG. 6 is a cross-sectional view showing the construction of the EGR valve in FIG. 5.
In FIGS. 5 and 6, exhaust gas conveyed from an exhaust pipe 3 connected to a combustion chamber 2 in an engine 1 is cooled by a cooler 4, then conveyed to an EGR valve 5 for regulating the recirculation of the exhaust gas to an intake pipe (not shown) in the engine 1. The flow amount of the exhaust gas is regulated by a regulating valve 6 disposed in the EGR valve 5 for regulating the opening of an exhaust gas passage in response to a negative-pressure signal from the intake pipe. This exhaust gas is resupplied to the intake pipe. In this manner, the exhaust gas is recombusted in the engine 1, thus reducing toxic nitrogen oxides in the exhaust gas. Moreover, the regulating valve 6 is operated by the pressure difference in a negative-pressure chamber 8 formed above a diaphragm 7.
A housing 10 is provided with an input port 11 connected to the exhaust pipe 3 of the engine 1, an output port 12 connected to the intake pipe of the engine 1, and a fluid passage 13 in which the exhaust gas which is the controlled fluid flows. Partway along the fluid passage 13, the regulating valve 6 contacting a valve seat 14 formed within the housing 10 is connected to a valve shaft 15 and slides within a shaft-bush 16 secured to the housing 10. A holder 17 disposed below the shaft-bush 16 in an upper portion of the fluid passage 13 prevents penetration by carbon or foreign matter contained in the exhaust gas.
Moreover, although not shown in the figures in some cases, penetration by carbon or foreign matter contained in the exhaust gas is prevented by disposing labyrinth packing, shielding, metal-fiber packing, and the like, inside the holder 17.
The diaphragm 7 is sandwiched by keep plates 20a, 20b, and the upper end 21 of the valve shaft 15 is mounted on the central portion thereof by crimping. A lower negative-pressure case 22 is disposed in close contact with an upper portion of the shaft-bush 16 and is attached to the housing 10 by a screw 23 through packing 27 described below. The negative-pressure chamber 8 is formed between the diaphragm 7 and an upper negative-pressure case 24 and negative pressure is introduced thereto from a negative-pressure source (not shown) by means of a negative-pressure inlet pipe 25 passing through and mounted on the upper negative-pressure case 24 which cooperates with the lower negative-pressure case 22 to hold the perimeter of the diaphragm 7 therebetween. Moreover, the regulating valve 6 connected to the valve shaft 15 is pressed downwards by a spring 26 disposed inside the upper negative-pressure case 24, but the diaphragm 7 may move upwards depending on the magnitude of the negative pressure conveyed to the negative-pressure chamber 8, and for that reason the regulating valve 6 may be driven upwards, varying the opening of the regulating valve 6. The packing 27 is interposed between the housing 10 and the lower negative-pressure case 22 and shuts out the heat from the housing 10.
In a construction having a single shaft-bush such as that in FIG. 6, because the amount of fluid controlled by EGR valves has increased with the strengthening of exhaust gas regulations, or because the amount of exhaust from truck engines 1 is large and the recirculation of exhaust gas by EGR valves for trucks is great, the need for large bores has increased even in the case of single regulating valves, and therefore, there has been a tendency for the weight on the end of the valve shaft to be problematic. FIG. 7 shows a control valve assembly in which both ends of a valve shaft having a regulating valve secured thereto are held by shaft-bushes or brace plates in order to improve linear-drive control valve assemblies in which stable retention against the vibrations, etc., of the internal combustion engine was difficult with only a single shaft-bush as above.
FIG. 7 is a cross-sectional view showing the construction of another conventional EGR valve such as that disclosed in Japanese Patent Application Laid-Open No. 58-37374, for example.
In the numbering used in FIG. 7, the same numbering as that used in FIG. 6 represents identical or corresponding parts. The construction shown in FIG. 7 has, in addition to the construction of FIG. 6, a valve shaft 15 connected to the regulating valve 6 extending beyond the regulating valve 6, an end portion 15a thereof being guided by insertion into the central boss 30a of a brace plate 30 secured to the housing 10.
Meanwhile, there may be large surges in the controlled fluid, and FIG. 8 shows a control valve assembly in which two regulating valves are disposed coaxially, so that the pressure of the controlled fluid is applied to the two regulating valves in mutually opposite directions in order to cancel out these surges. In this construction, the valve shaft securing the regulating valves must be lengthened.
FIG. 8 is a cross-sectional view showing the construction of a conventional ISC valve such as that disclosed in Japanese Utility Model Application Laid-Open No. 58-4759, for example.
In the numbering used in FIG. 8, the same numbering as that used in FIG. 6 or 7 represents identical or corresponding parts. The ISC valve shown in FIG. 8 has a valve shaft 15 contacting a plunger rod 32 moved linearly by a solenoid coil 31, and two regulating valves 6 connected thereto. Because the length of extension of the valve shaft 15 beyond the shaft-bush 16 secured to the housing 10 on the solenoid coil 31 side is particularly large and cannot be supported by the shaft-bush 16 alone, an end portion 15a of the valve shaft 15 at the opposite end from that contacting the solenoid coil 31 being the drive source for opening and closing the regulating valve 6 is guided by insertion into the central boss 30a of the brace plate 30, in the same way as in FIG. 7, with the aim of stabilizing sliding. In addition, in order to avoid deterioration of sliding due to carbon or foreign matter contained in the controlled fluid penetrating the sliding portion between the valve shaft 15 and the shaft-bush 16 or the sliding portion between the central boss portion 30a and the end portion 15a, the central boss portion 30a of the brace plate 30 constructed in the fluid passage 13 is constructed such that a shielding material 33 capable of expanding and contracting freely relative to the linear motion so as not to affect the sliding covers the shaft-bush 16 on the side nearest to the fluid passage 13, or the central boss portion 30a and the end portion 15a. 
However, because conventional EGR valves and ISC valves have had the above constructions, they have suffered from the problems described below.
In a control valve assembly in which both sides of the regulating valve secured to the valve shaft are held by bushes or brace plates in order to achieve linear motion stabilized against the vibrations of the internal combustion engine, etc., the shaft-bush holding the valve shaft connected to the diaphragm or the solenoid coil being the drive source for opening and closing the regulating valve and the brace plate disposed on the opposite side are installed in the fluid passage. For that reason, when the controlled fluid contains carbon or foreign matter, carbon or foreign matter penetrates the sliding portion between the central boss portion of the brace plate and the valve shaft.
In addition, since the central boss portion of the brace plate is installed in the fluid passage, a blind recess is formed making it difficult to flush out any foreign matter which has penetrated. Furthermore, when the controlled fluid is a high-temperature gas, the gas is cooled in the small gap formed by the blind recess, facilitating the formation of condensation, and there is a risk that corrosion or solidification of any foreign matter which has penetrated will obstruct stable sliding of the valve shaft.
Furthermore, in a construction in which both ends of the valve shaft are slidably held by rigid valve bushes or brace plates, concentricity is required between the shaft-bush and the central boss portion of the brace plate in order to ensure stable sliding of the valve shaft, making high-precision machining necessary. Otherwise, if high-precision machining is not used, it has been difficult to ensure stable sliding of the valve shaft without reducing the precision of the valve shaft support by enlarging the space between the central boss portion and the valve shaft.
Consequently, the present invention aims to provide a control valve assembly enables a valve shaft to maintain good sliding even when a controlled fluid contains carbon or foreign matter.
Furthermore, the present invention additionally aims to provide a control valve assembly for an internal combustion engine enabling stable shaft positioning and holding performance relative to the linear motion of the valve shaft.
The present invention comprises a fluid passage disposed inside a housing, a regulating valve disposed inside the fluid passage for regulating the flow of a controlled fluid flowing through the fluid passage, a valve shaft for supporting the regulating valve, and an actuator disposed at one end of the valve shaft for opening and closing the regulating valve by actuating the valve shaft, a first shaft-bush mounted to the housing on one side of the regulating valve for slidably supporting the valve shaft, and an elastic second shaft-bush held on the housing by a holding member on the opposite side of the regulating valve for slidably supporting the valve shaft. Thus, even if carbon or foreign matter contained in the controlled fluid accretes between the valve shaft and the second shaft-bush, good sliding between the valve shaft and the second shaft-bush can be maintained with the carbon or foreign matter being scraped away by a small sliding resistance, and misalignment of the axes between the first shaft-bush and the second shaft-bush can be absorbed, the need for high-precision machining in the second shaft-bush can also be eliminated, and further stable shaft positioning and holding performance can be achieved.
The present invention may also comprise a second shaft-bush formed from fine metal wire. Thus, because the valve shaft and an inside diameter portion of the second shaft-bush are placed in contact with each other with elastic and uniform force, the valve shaft can slide on the minimal surface area of the fine metal wire. Furthermore, even if high-viscosity carbon and foreign matter in the exhaust gas composed of components with a range of molecular weights accretes between the valve shaft and the second shaft-bush, the carbon or foreign matter can be scraped away by the small sliding resistance, and misalignment of the axes between the first shaft-bush and the second shaft-bush can be absorbed, the need for high-precision machining in the second shaft-bush can also be eliminated, and further stable shaft positioning and holding performance can be achieved. In addition, since the flow around the second shaft-bush portion is improved, even if the controlled fluid is a high-temperature gas, the occurrence of condensation by cooling of the gas is prevented, enabling the suppression of corrosion or the solidification of any foreign matter which has penetrated.
The present invention may also be provided with a recess on the opposite side of the second shaft-bush from the fluid passage. Thus, even if carbon or foreign matter contained in the controlled fluid accretes between the valve shaft and the second shaft-bush, it can be scraped away by the second shaft-bush and allowed to accumulate in the recess.
In the present invention, the holding member may also be provided with at least one aperture for circulation through the fluid passage and the recess portion. Thus, since most of the controlled fluid flows through the aperture, the amount of carbon and foreign matter in the controlled fluid flowing between the valve shaft and the second shaft-bush can be reduced.
In the present invention, the holding member may be designed such that the second shaft-bush is removably mounted. Thus, the holding member can be mounted to the second shaft-bush before the holding member is installed in the housing, reducing the attention required when conveying or handling the second shaft-bush, a body shaped from fine metal wire, thereby enabling the assembly operation to be improved, and weight to be reduced.
In the present invention, the recess may be designed so as to be removably mounted. Thus, carbon or foreign matter from the controlled fluid which has accumulated in the recess can be removed.
The present invention may also comprise a fluid passage disposed inside a housing, a regulating valve disposed inside the fluid passage for regulating the flow of a controlled fluid flowing through the fluid passage, a valve shaft for supporting the regulating valve, an actuator for opening and closing the regulating valve by actuating the valve shaft, and an elastic shaft-bush mounted to the housing for supporting the valve shaft at least one point so as to slide freely. Thus, even if carbon or foreign matter contained in the controlled fluid accretes between the valve shaft and the second shaft-bush, good sliding of the valve shaft can be maintained, and misalignment of the axes between the shaft-bushes bush can be absorbed when a plurality of shaft-bushes are used, the need for high-precision machining in the elastic shaft-bush can be eliminated, and stable shaft positioning and holding performance can be achieved.